I think it was originally on Forge based on my memory where I was disappointed after seeing the trailer and trying to play with it. I couldn't though since I was using Fabric and didn't want to use Forge.
No, I always remember it being a forge mod, since the 1.15 days at least. Not sure what to tell you. Maybe they discussed Fabric but went with Forge in the early stages? Maybe you're thinking of being frustrated with it not being a Fabric mod and having to install Forge? Maybe you're thinking of another mod entirely?
Others have already answered, but just to confirm as a big Create fan, no it was not originally a Fabric mod. I played with it on Forge since the early versions on 1.14 and I remember eagerly awaiting a Fabric release.
I remember it being on 1.14 first while a lot of mods skipped that version and went straight to 1.15 I was frustrated that I wanted to do things with create on a 1.15 modpack but couldn't